The present invention relates to linear polymers of ferrocene and a process for making such polymers. The polymers are useful for the formation of novel metal chelates which are exceptionally stable catalysts for use in a hydroformylation process. Furthermore because of the highly linear nature of the ferrocene polymers, the catalysts are homogeneous under a wide variety of reaction conditions yet may be easily rendered insoluble for recovery purposes.
D. Seyferth and H. P. Withers in Journal of Organometallic Chemistry, 185, C1-5 (1980) disclosed certain mono- and bidentate ligands, including 1-diphenylarsino-1'-diphenylphosphinoferrocene. Also disclosed was the fact that phosphino- or arsinoferrocene polymers capped at one end with lithium and at the other end with an organic moiety can be prepared by reacting (1,1'-ferrocenediyl)phenylphosphine or (1,1'-ferrocenediyl)phenylarsine with a stoichiometric deficiency of an organolithium reagent. Subsequent efforts to produce high molecular weight polymeric materials by means of this process have resulted in oligomers of up to about five units but no higher polymeric materials have been observed.
The reaction of ferrocene with phenyldihalophosphines to produce polymeric products has been studied by C. U. Pittman, Jr., J. Pol. Sci. A-1, 5, 2927-2937 (1967), and E. W. Neuse et al., J. Macromol. Sci. (Chem) A-1, 3, 371-386 (1967). The polymers formed were of the formula: ##STR1## respectively.
The polymers formed were of relatively low molecular weight having number average molecular weights less than 4000 amu, and less than 6500 upon subfractionation. The polymers also were reported to contains cross-linking formed by the non-selective reaction of more than two phenyldihalophosphines with certain ferrocene moieties. The references further described "heteroannular polymerization", the process resulting from cleavage of ferrocene rings by the action of hydrogen chloride produced in situ and the subsequent incorporation of moieties other than ferrocene and phosphine into the polymer structure. The principal heteroannular moiety is cyclopentylene.
Polymers prepared according to the prior art processes by the Lewis acid-catalyzed polycondensation of ferrocene contained appreciable amounts of such cyclopentylene or related groups in the polymeric structure. The presence of such cyclopentylene groups in the polymer tends to reduce the polymer's thermal stability and otherwise deleteriously affect the polymer's qualities.
It would be desirable to produce a polymeric ferrocenyl derivative of relatively high molecular weight which is linear and which is substantially free from heteroannular polymerized moieties.